Impacts and Extinctions: Understanding Earth's Place in Space

1. Chapter 14 Impacts and Extinctions

2. Learning Objectives Know the difference between asteroids, meteoroids, and comets Understand the physical processes associated with airbursts and impact craters Understand the possible causes of mass extinction Know the evidence for the impact hypothesis that produced the mass extinction at the end of the Cretaceous period

3. Learning Objectives, cont. Know the likely physical, chemical, and biological consequences of impact from a large asteroid or comet Understand the risk of impact or airburst of extraterrestrial objects and how that risk might be minimized

4. Earth’s Place in Space Origins of universe begin with “Big Bang” 14 billion years ago Explosion producing atomic particles First stars probably formed 13 billion years ago Lifetime of stars depends on mass Large stars burn up more quickly ~100,000 years Smaller stars, like our sun, ~10 billion years Supernovas signal death of star No longer capable of sustaining its mass and collapses inward Explosion scatters mass into space creating a nebula Nebula begins to collapse back inward on itself and new stars are born in a solar nebula

5. Earth’s Place in Space, cont. Five billion years ago, supernova explosion triggered the formation of our sun Sun grew by buildup of matter from solar nebula Pancake of rotating hydrogen and helium dust After formation of sun, other particles were trapped in rings Particles in rings attracted other particles and collapsed into planets Earth was hit by objects that added to its formation Bombardment continues today at a lesser rate

6. Figure 14.2

7. Figure 14.4

8. Asteroids, Meteroids, and Comets Particles in solar system are arranged by diameter and composition Asteroids Found in asteroid belt between Mars and Jupiter Composed of rock, metallic, or combinations Meteoroids are broken up asteroids Meteors are meteoroids that enter Earth’s atmosphere Burn and create “shooting stars” Comets have glowing tails Composed of rock surrounded by ice Originated in Oort Cloud beyond the Kuiper Belt

9. Table 14.1

10. Figure 14.3

11. Airbursts and Impacts Objects enter Earth’s atmosphere at 12 to 72 km/s (27,000 to 161,000 mph) Metallic or stony Heat up due to friction as they fall through atmosphere, produce bright light and undergo changes Meteorites If the object strikes Earth Concentrated in Antarctica Airbursts Object explodes in atmosphere 12 to 50 km (7 to 31 mi.) Ex: Tunguska

12. Figure 14.7

13. Impact Crater Provide evidence of meteor impacts, i.e., Barringer Crater in Arizona Bowl shaped depressions with upraised rim Rim is overlain by ejecta blanket, material blown out of the crater upon impact Broken rocks cemented together into Breccia Features of impact craters are unique from other craters Impacts involve high velocity, energy, pressure and temperature Kinetic energy of impact produces shock wave into earth Compresses, heats, melts and excavates materials Rocks become metamorphosed or melt with other materials

14. Figure 14.8

15. Simple Impact Craters Typically small < 6 km (4 mi.) Ex. Barringer Crater Figure 14.9b

16. Complex Impact Craters Larger in diameter > 6 km (4 mi.) Rim collapses more completely Center uplifts following impact Figure 14.10b

17. Impact Craters, cont. Craters are much more common on Moon Most impacts are in ocean buried or destroyed Impacts on land have been eroded or buried by debris Smaller objects burn up in Earth’s atmosphere before impact

18. Table 14.2

19. Mass Extinctions Sudden loss of large numbers of plants and animals relative to number of new species being added Defines the boundaries of geologic periods or epochs Usually involve rapid climate change, triggered by Plate Tectonics Slow process that moves habitats to different locations Volcanic activity Flood basalts produce large eruptions of CO2, warming Earth Silica-rich explosions produce volcanic ash that reflects radiation, cooling Earth Extraterrestial impact or airburst

20. Table 14.3

21. Six Major Mass Extinctions Ordovician, 446 mya, continental glaciation in Southern Hemisphere Permian, 250 mya, volcanoes causing global warming and cooling Triassic-Jurassic boundary, 202 mya, volcanic activity associated with breakup of Pangaea Cretaceous-Tertiary boundary (K-T boundary), 65 mya, Asteroid impact Eoceneperiod, 34 mya, plate tectonics Pleistocene Epoch, initiated by airburst, continues today caused by human activity

22. Figure 14.13

23. K-T Boundary Mass Extinction Dinosaurs disappeared with many plants and animals 70 percent of all genera died Set the stage for evolution of mammals First question, What does geologic history tell us about K-T Boundary? Walter and Luis Alvarez decided to measure concentration of Iridium in clay layer at K-T boundary in Italy Fossils found below layer were not found above How long did it take to form the clay layer? Iridium deposits say that layer formed quickly Probably extinction caused by single asteroid impact

24. K-T Boundary Mass Extinction, cont. Alvarez did not have a crater to prove the theory Crater was identified in 1991 in Yucatan Peninsula Diameter approx. 180 km (112 mi.) Nearly circular Semi-circular pattern of sinkholes, cenotes, on land defining edge Possibly as deep as 30 to 40 km (18 to 25 mi.) Slumps and slides filled crater Drilling finds breccia under the surface Glassy indicating intense heat

25. Figure 14.15

26. Sequence of Events Asteroid moving at 30 km (19 mi.) per second Asteroid impacts Earth produces crater 200 km (125 mi.) diameter, 40 km (25 mi.) deep Shock waves crush, melt rocks, vaporized rocks on outer fringe Figure 14.16a Figure 14.16b

27. Sequence of Events, cont. 1 Seconds after impact Ejecta blanket forms Mushroom cloud of of dust and debris Fireball sets off wildfires around the globe Sulfuric acid enters atmosphere Dust blocks sunlight Tsunamis from impact reached over 300 m (1000 ft.) Figure 14.16c

28. Sequence of Events, cont. 2 Month later No sunlight, no photosynthesis Continued acid rain Food chain stopped Several months later Sunlight returns Acid rain stops Ferns restored on burned landscape Figure 14.16d Figure 14.16e

29. K-T Extinction, Final Impact caused massive extinction, but allowed for evolution of mammals Another impact of this size would mean another mass extinction probably for humans and other large mammals However, impacts of this size are very rare Occur once ever 40 to 100 my Smaller impacts are more probable and have their own dangers

30. Linkages with Other Natural Hazards Asteroid impact is linked with a variety of hazards such as: Tsunami if the impact is in water Wildfires from heat from impact Earthquakes from shock waves from impact Mass Wasting from earthquakes and impact Climate Change from debris Volcanic Eruptions melting and instability in mantle

31. Risk Related to Impacts Risk related to probability and consequences Large events have consequences will be catastrophic Worldwide effects Potential for mass extinction Return period of 10’s to 100’s of millions of years Smaller events have regional catastrophe Effects depends on site of event Return period of 1000 years Likelihood of an urban area hit every few 10,000’s years

32. Risk Related to Impacts, cont. Risk from impacts is relatively high Probability that you will be killed by Impact: 0.01 to 0.1 percent Car accident: 0.008 percent Drowning: 0.001 percent However, that is AVERAGE probability over thousands of years Events and deaths are very rare!

33. Minimizing the Impact Hazard Identify nearby threatening objects Spacewatch Inventory of objects with diameter > 100 m in Earth crossing orbits 85,000 objects to date Near-Earth Asteroid Tracking (NEAT) project Identify objects diameter of 1 km Use telescopes and digital imaging devices Most objects threatening Earth will not collide form several 1000’s of years from discovery

34. Minimizing the Impact Hazard, cont. Options once a hazard is detected Blowing it up in space Small pieces could become radioactive and rain down on earth Nudging it out of Earth’s orbit Much more likely since we will have time to study object Technology can change orbit of asteroid Costly and need coordination of World military and space agencies Evacuation Possible if we can predict impact point Could be impossible depending on how large an area would need to be evacuated

35. End Impacts and Extinctions Chapter 14